Recording of sound



Aug.- 24, 1937. ND 2,690,753

RECORDING OF SOUND Filed Oct. 16, 1936 Snventor Berihold FPeund By I vGttorneg Patented Aug. 24, 1937 mart RECORDING OF SOUND Application()ctober 16, 1936, Serial No. 105,846 In Germany July 30, 1935 4 Claims.

This invention relates to the recording of sound, and has for itsprincipal object the provision of an improved recording system andmethod of operation whereby the difficulties heretofore en- 5 counteredin the operation of anti-ground-noise systems are avoided.

It is known to record sound by systems involving the use of agalvanometer or light valve actuated in accordance with the audiofrequency to be recorded and to further subject these recording elementsto a current which is varied as the volume of the recorded signals forthe purpose of eliminating the background noise otherwise produced bythe transparent portion of the record. The operation of such systemssometimes involves the dilficulty that the influence of the volumeresponsive current must be exerted gradually to avoid the production ofspurious sounds and must be exerted quickly enough to preventcutting-01f of the recorded peaks.

It has been attempted to avoid this difiiculty by recording the sound ona single track without the use of volume responsive current andutilizing such current subsequently during the rerecording operation.This procedure, however, has the disadvantage that the background noiseis likely to be rerecorded together with the desired sound.

In accordance with the present invention these difliculties are avoidedby a procedure which involves first recording the sound in the form of apush-pull record and subsequently rerecording from this push-pull recordto a single track record which is at the same time subjected to ashading effect dependent on a volume responsive current which may bederived either from the push-pull record or from the original source ofsound.

The invention will be better understood from the following descriptionwhen considered in connection with the accompanying drawing and itsscope will be indicated by the appended claims.

Referring to the drawing,

Fig. 1 illustrates a system arranged in accordance with the invention,

Fig. 2 is similar to Fig. 1 in some respects but difiers therefrom withrespect to the size of the photocell utilized to pick up the volumeresponsive current, and

Fig. 3 illustrates the application of the invention to the production ofa variable density record.

The system of Fig. 1 includes a microphone I or other pick-up device onwhich are impressed 55 the sounds to be recorded. Upon the lightsensiappears black or dark.

tive film 3 are produced by means of a push-pull recorder 2 a push-pullsound record wherein the positive and negative half cycles are recordedon separate tracks which are spaced from one another in accordance witha known method of 5 push-pull recording. These tracks are rerecordedupon a film in the form of a single sound track 6 by means of photocells4 and 5, which are connected in push-pull. In addition to the cells 4and 5, a photoelectric cell 1 shown as extending 1 entirely across thesound record, is utilized to produce a volume responsive current throughwhich a background noise reduction track is produced.

The arrangement of Fig. 2 differs from that 15 just described in that aphotoelectric cell it is provided with a width A so great that thedesired gradual increase and decrease of the volume responsive ornoiseless sound track is automatically produced. It is essential thatthe push-pull re- 20 producers 1 and 5 and the anti-noise reproducers lor H) be so spaced longitudinally of the pushpull record as to producethe proper relation between sound track 6 and the anti-noise track 8.

The system of Fig. 3 is designed for the noiseless rerecording to asound record of the variable density type as distinguished from thevariable area type record of Figs. 1 and 2. In this case, the currentssupplied from cells 4 and 5 and from the cell 7 are superposed and usedfor the combined recording of the cell track and the antibackgroundnoise track. The joint recording device is indicated at E5 and may be ofany of the many suitable forms known to those skilled in the art. It isadvantageous to have the primary push-pull record 3 recorded positivefor the reason that the sound modulations appear light or transparentand the remainder of the record This is easily accomplished by asuitable adjustment of the recording apparatus. In that case, theseparate copy of the push-pull record as a positive is not necessary inorder to efiect the transformation to the noiseless or background noisetrack in accordance with the invention. In accordance with theinvention, noiseless master records in standard noiseless track form maybe produced and it is particularly feasible to obtain noiseless masterrecords that may be directly copied, for instance, the recordedpush-pull variable width track by means of a single transformation, ifnecessary, for the insertion of suitable correcting means.

It will be readily understood that the pushpull photocells 4 and 5 andthe volume responsive current cell 1 or ID are so spaced with respect toone another longitudinally of the film that a proper cooperativerelation may be maintained between the single track 6 and the anti-noisetrack 8. It will also be apparent that only half the width of theprimary record may be utilized to derive the volume responsive currentand other modifications may be made without departing from the spiritand scope of the invention.

I claim as my invention:

1. The combination of means for recording sound in the form of apush-pull record having the positive and negative half cycles spacedfrom,

element responsive to said positive and negative half cycle records forproducing an anti-noise track in cooperative relation with said singletrack.

3. The combination of means for recording sound in the form of apush-pull record having the positive and negative half cycles spacedfrom one another, means for rerecording said sound from said push-pullrecord to a single track record, and means including a light responsiveelement of relatively great width for rerecording in cooperativerelation with said single track.

4. The combination of means for recording sound in the form of apush-pull record having the positive and negative half cycles spacedfrom one another, means for rerecording said sound from said push-pullrecord to a single track record, and means including a light responsiveelement spaced from said push-pull means for producing an anti-noisetrack in cooperative rela- H tion with said single track.

BER'I'HOLD FREUND.

